The present invention is directed to power generating devices for bicycles and, more particularly, to claw-pole dynamos mounted in a bicycle hub.
An example of a conventional claw-pole power generator is described in Japanese Unexamined Patent Application (Kokai) 8-192784. In the power generator 10 described therein, two iron-core members 15 are combined with each other such that the pole shoes 15a and 15b disposed along the corresponding outer peripheries are adjacent to each other. The central portions of these iron-core members 15 are drawn (as shown in FIG. 2 of the Application), and the inner peripheral ends of the two combined iron-core members 15 are brought into contact with each other. Magnetic flux is thereby transmitted by the inner peripheral portions of the iron-core members located inside an annular coil 14, thus causing an electric current to pass through the coil 14 under the action of the alternating flux induced therein.
Considerable eddy currents are induced by the axial alternating flux in the two iron-core members when the inner peripheral portions of the iron-core members are narrowed, brought into contact with each other and coupled magnetically, as described above. Much of the power generated is therefore consumed as core loss, resulting in diminished power output.
Linking the inner peripheral portions of both iron-core members with separate members have been suggested for obtaining a structure that possesses reduced core loss. In such a structure, however, eddy currents are induced inside the iron-core members and the separate members, further lowering the efficiency of power generation. In the particular case of a power generator in which the input rotation has a low speed, such as a power supply for a bicycle lamp or a wind-powered generator for household use, a reduction in the power generation efficiency would be disadvantageous in that it would require a bulkier power generator or a stronger rotational force for power generation.
The present invention is directed to a claw-pole dynamo wherein eddy current are suppressed during power generation so as to improve the power generation efficiency of the dynamo. In one embodiment of the present invention, a claw pole dynamo includes an annular member having a magnet extending in a circumferential direction thereof for rotation around an axis; a first stator yoke having a first annular portion and a plurality of first pole shoes extending in a direction of the axis and in close proximity to the magnet, wherein the first annular portion defines a plurality of first discontinuities (such as slots) in a circumferential direction thereof; a second stator yoke having a second annular portion and a plurality of second pole shoes extending in the direction of the axis and in close proximity to the magnet, wherein the plurality of first pole shoes are interleaved with the plurality of second pole shoes in the circumferential directions of the first and second annular portions; a core yoke for magnetically coupling the first stator yoke and the second stator yoke and for transmitting a magnetic flux in the direction of the axis; and a coil disposed around the core yoke. The plurality of discontinuities suppress the eddy currents in the first stator yoke. If desired, the second stator yoke could have a similar plurality of discontinuities in the second annular portion thereof.
In another embodiment of the present invention, a claw pole dynamo includes an annular member having a magnet extending in a circumferential direction thereof for rotation around an axis; a first stator yoke having a first annular portion and a plurality of first pole shoes extending in a direction of the axis and in close proximity to the magnet; a second stator yoke having a second annular portion and a plurality of second pole shoes extending in the direction of the axis and in close proximity to the magnet; wherein the plurality of first pole shoes are interleaved with the plurality of second pole shoes in the circumferential direction; a core yoke for magnetically coupling the first stator yoke and the second stator yoke and for transmitting a magnetic flux in the direction of the axis; a coil disposed around the core yoke; and a first separation member disposed between the first stator yoke and the core yoke. If desired, the first separation member may include a plurality of discontinuities in a circumferential direction thereof to suppress eddy currents. A second separation member with or without a similar plurality of discontinuities may be disposed between the second stator yoke and the core yoke to further suppress eddy currents.
In yet another embodiment of the present invention, a claw pole dynamo may include an annular member having a magnet extending in a circumferential direction thereof for rotation around an axis; a first stator yoke having a first annular portion and a plurality of first pole shoes extending in a direction of the axis and in close proximity to the magnet; a second stator yoke having a second annular portion and a plurality of second pole shoes extending in the direction of the axis and in close proximity to the magnet; wherein the plurality of first pole shoes are interleaved with the plurality of second pole shoes in the circumferential direction; a core yoke for magnetically coupling the first stator yoke and the second stator yoke and for transmitting a magnetic flux in the direction of the axis; wherein the core yoke includes a plurality of sections disposed at different positions in a circumferential direction of the core yoke; and a coil disposed around the core yoke. The plurality of sections in the core yoke help to suppress eddy currents in the core yoke.